An aircraft skin is a thin sheet that covers all or a portion of the exterior of the aircraft. The aircraft skin is directly contacted by the air flow as the aircraft flies through the air, and is heated by the friction between the air flow and the skin material. For aircraft flying at relatively slow speeds, the frictional heating is not great, but with increasing aircraft speeds the maximum skin temperature is correspondingly increased. The material that forms the aircraft skin must have acceptable properties at the local maximum skin temperature, and the service temperature of the skin material is one of the potential limiting considerations in aircraft design.
Historically, aircraft skins have been made of aluminum alloys, which work well for aircraft flying at low speeds or higher speeds for short periods of time. More recently, some aircraft skins have been made of composite materials having better mechanical properties per unit weight than aluminum alloys at room temperature or slightly elevated temperatures. Aircraft skins have also been made of titanium alloys having service temperatures that are higher than those of aluminum alloys and composite materials, allowing the aircraft to operate at higher skin temperatures and thence higher sustained speeds than those having aluminum or composite aircraft skins.
Yet more-advanced aircraft have the potential for hypersonic flight wherein the aircraft skin, or portions thereof, are heated to even higher temperatures than permitted using the most advanced titanium-alloy aircraft skins now available. Alloys and intermetallic compounds are known that could be used to meet the aircraft skin requirements of these advanced aircraft, but these alloys and intermetallic compounds cannot be fabricated into the required sheet form using existing practices. Sheet material is normally made by melting the material, casting an ingot of the material, and then rolling the material to the form of the sheet. The metallic alloys and intermetallic compounds that could meet the property requirements for the sheet skins of the advanced aircraft do not exhibit the necessary ductility to permit them to be rolled into sheet form in a commercially viable operation. As a result, these low-ductility materials are not candidates for thin-sheet applications such as aircraft skins at this time.
There is accordingly a need for a combination of material and processing that permits the production of sheets suitable for aircraft skins that are subjected to the highest operating temperatures. The present invention fulfills this need, and further provides related advantages.